This invention relates to a catalyst which is useful in the production of elastomeric, primarily isotactic polyolefins and a process for producing such polymers using said catalyst.
U.S. Pat. No. 4,335,225, issued Jun. 15, 1982, discloses a fractionable elastic polypropylene which is said to have an isotactic content of 55% or less and also to contain some syndiotactic and atactic polypropylene. This patent, and its companions on the catalyst system for making this elastic polypropylene, contain much information about elastic type polypropylene compositions, although the researchers at Montecatini, especially including Giulio Natta, produced some polypropylene compositions which exhibited the same elastomeric characteristics. Specifically, U.S. Pat. Nos. 3,175,999; 3,257,370 and 3,258,455 disclose polypropylene compositions which have elastic type properties. Similarly the researchers at Standard Oil, especially including Donald Emrick, had produced polypropylene compositions which exhibited the same elastomeric characteristics. Specifically U.S. Pat. No. 3,278,512 dicloses primarily isotactic polypropylene compositions which have elastic type properties.
Elastomeric polypropylene is different from the "normal" or more well known polypropylenes. These more well known types are crystalline and amorphous polypropylenes. It is normally accepted that crystalline polypropylene generally has the isotactic or syndiotactic structure and that amorphous polypropylene generally has considerable atactic (sometimes designated as heterotactic) structure. Giulio Natt's U.S. Pat. Nos. 3,112,300 and 3,112,301 describe isotactic polypropylene and give structural formulae for isotactic and syndiotactic polypropylene. The former is a straight chain of propylene units wherein the methyl groups are all aligned on one side of the polymer chain. In the latter, the methyl groups alternate from one side of the chain to the other. In static (heterotactic) polypropylene, the methyl groups are arranged randomly on the two sides of the chain.
Almost all of the polypropylene which is used commercially is highly crystalline polypropylene. These products are well known and have been the subject of many patents and articles. Amorphous polypropylenes, which have very little strength, are used commercially primarily in adhesives and asphalt additives.